Large floating ocean platform

ABSTRACT

A station keeping apparatus for large floating ocean platforms. The arrangement makes use of wave energy acting on a platform supported by buoyancy derived from the submergence of long vertical columns. The oscillating horizontal component of stream flow in a predominant wave train yields a hydrodynamic force acting on such vertical columns if the latter possesses appropriately profiled cross-sections oriented to the wave flow pattern. A series of such columns can be arranged so that the resultant average hydrodynamic force vector will directly oppose the predominant wind and current vectors which tend to disturb the positioning of the platform.

United States Patent l l l l l 1 3,762,352

Brahtz I 1 Oct. 2, 1973 LARGE FLOATING OCEAN PLATFORM Primary Examiner-Milton Buchler 1751 lnventor: John F. Peel Brahtz, LaJolla, Calif. f" M- Attorney-Richard S. Sclascla et al.

[73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC. [57] 3 ABSTRACT [22] Filed: Feb. 24, 1972 A station keeping apparatus for large floating ocean platforms. The arrangement makes use of wave energy PP 228,933 acting on a platform supported by buoyancy derived from the submergence of long vertical columns. The

521 US. Cl 114/0.5 D oscillating mizomal compmem Stream a [51] Int. Cl B63b 35/00 P?dominant wave P Yields hydrodynamic [58] Field of Search 114/.5 D, .5 BD, ting Such columns f the POSSSes 114/435; 61/465 appropriately profiled cross-sectlons oriented to the wave flow pattern. A series of such columns can be ar- [56] References Cited anged so thatll :jhe resultant avlerage dhyd 'odynami:

orce vector wl lrect y oppose t e pre omlnant win 3 273 526 :T E PATENTS l 14/ 5 D and current vectors which tend to disturb thepositionosten 3,673,973 7/1972 Glosten ll4/43.5 X mg of the platform.

3 Claims, 8 Drawing Figures PAIENIEDDIZI ems v SHEET 1III 2 Fig.

WAVE PROPAGATION F' DRAG FORCE DRAG COEFFICIENT C' LIFT COEFFICIENT C' Fig. 3.

DRAG FORCE DRAG COEFFICIENT CD LIFT COEFFICIENT CL PAIEIIIEIIIIII'Z 3.762.352

SHEET 2 [IF 2 [-7 5 FL LIFT FORGE Fi 6 [F1 LIFT FORGE DRAG COEFFICIENT CO DRAG COEFFICIENT Ci: LIFT COEFFICIENT CI. LIFT COEFFICIENT C'L C L O Fig. 7.

T CINIM y I /I0 /I2 TYPICAL suPPORTING COLUMN ORIENTATION IN ARRAY FOR ROTATING PLATFORM IN CLOCKWISE SENSE C TO A WINDWARD BEARING ANO MINIMUM ADVERSE WIND ORAG.

, IX I Fig. 8.

COMPUTER SENSOR IB- IG 1 LARGE FLOATING OCEAN PLATFORM BACKGROUND OF THE INVENTION ocean area. Theconventional means for maintaining such surface location includes spread moorings, and deep taut line moorings. However, very large lines and anchorsv may be required depending on the size of the ocean floating structures.

However, if the wave drag can be utilized to provide force vectors which oppose the wind and current vectors that tend to disturb the specific positioning of the platform, the mooring requirements thereof will be reduced or perhaps even eliminated.

SUMMARY OF THE INVENTION The present disclosure describes such an invention which advantageously uses net wave energy produced by proper orientation of vertical non-symmetric columns against the direction of wave propagation. A multiplicity of columns are attached to the under surface of a large platform and each possesses a crescent shaped cross section. The extracted energy is-employed to reduce or eliminate the need for an expensive and variable mooring and propulsion mechanism.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing a platform supported on vertical columns.

,FIG. 2 is an enlarged detail side elevational view of a pair of supporting columns illustrating the rotational fluid motion in the wave system interacting with the columns.

FIGS. 3 and 4 are sectional views along lines 3-3 and 4-4 respectively of FIG. 2 showing the specially shaped columns and the alternatinghydrodynamic drag forces attending the oscillating flow.

FIGS. 5 and 6 are sectional views similar to FIGS. 3 and 4 with'the columns rotated 90 about their axis to show the lift forces.

FIG. 7 is a typical supporting column orientation for rotating the platform of the invention in a clockwise direction. to

FIG. 8 is a schematic view of the mechanism for controlling a supporting column.

DESCRIPTION OF THE PREFERRED EMBODIMENT a crescent shaped cross-section as shown-in FIGS. 2

thru 7 with each column being properly oriented against the direction of wave propagation to extract the wave energy produced. Such energy is used to reduce or eliminate the need for unreliable mooring and propulsion apparatus. The supporting columns 12 are either movable or fixed. If fixed, proper positioning of the platform 10 allows maximum hydrodynamic force vectors to be developed which oppose the natural vectors tending o disturb the platform.

If the vertical support columns 12 for an ocean platform 10 are considered a cantilevered hydrofoil in a train of traveling ocean surface waves, the horizontal projection of the rotational fluid motion in the wave system interacting with the column profile would appear as a two-dimensional oscillating flow shown best in FIG. 2. The alternating hydrodynamic drag forces attending the oscillating flow in general would be unequal for reverse directions as shown in FIGS. 3 and 4. Moreover, if the sectional profile of column 12 has its single axis of symmetry parallel to the wave velocity, the transverse lift coefficients in the horizontal plane would be zero for either of the opposing directions of symmetrical flow, FIGS. 3 and 4. However if the vertical support columns are rotated about their vertical axis through from its position-of symmetry with re.- spect to the oscillating wave motion, the fore and aft drag coefficients would become equal and the lift coefficients in the two opposing directions of flow would be greater than zero, FIGS. 5 and 6.

The magnitude of wave energy available for propulsive purposes is proportional to the transverse lift coefficient or the difference between opposing unequal drag coefficients for the column hydrofoil 12 in any particular oscillating flow field; Consequently, a useful propulsive thrust or for that matter a significant lift force within the oscillating wave motion is developed for either of the opposing directions parallel to the wave velocity or for either of the opposing directions normal to the wave velocity.

The crescent profile as illustrated in FIGS. 3 through 6 offers in the most practicalway a manner of obtaining a large difference in reversed alternate drag coefficients while also affording the design opportunity for optimizing the combination of structural and hydrodynamic properties for the supporting columns 12. Also the crescent profile offers approximately a-two-to-one ratio for drag coefficients in opposing flow directions.

Assuming the lift properties of the support columns 12 are not exploited, the principle formanaging the direction of wave induced drag forces so asto serve the platform 10 positioning requirements, involves either seeking to maximize the sum of horizontal moment couples acting on the total column array or otherwise seeking to maximize the sum of aligned and polarized forces so as to develop the largest possible propulsive thrust. The need for developing an effective turning couple by maximizing applied moments acting on the platform 10 would arise with the need to orient the platform 10 most advantageously to the prevailing-adverse wind. Having oriented the platformmostadvantageouslyto the wind, the wave-induced dragforces-on individual supporting columns 12 can thenbe polarized so as to provide the greatest possible force component opposing the combined adverse wind and'water currents. Often patterns'of wind-driven ocean currentsand ocean surface wave trains conform to the prevailing wind streams,

Such conditions ideally provide maximum opportunity for polarizing the column hydrofoil forces so as to directly oppose the adverse steady state wind and water currents. Normally, only that component of combined adverse drag forces resulting from wind and water current which is directly opposed and equal or less than the wave-induced propulsive drag force can be nullified for station keeping purposes. However, a larger station keeping thrust directly opposing adverse wind and water current drag can be developed by employing an array of support columns including both an idealized drag profile and an idealized lift profile. By properly integrating the directional orientation of each lift or drag column within the array, the propulsive thrust opposing any resultant adverse wind and water drag regardless of bearing can be maximized.

In order that the supporting columns 12 may be best utilized for purposes of maximizing either propulsive thrust or turning movement, each vertical column 12 will require a suitable rotating mechanism such as a worm gear assembly 14. As shown in FIG. 8, a sensing device 16 may be employed to determine the direction of and changes in wave energy with the signal obtained being relayed to a computer 18 which operates motor 20 to rotate worm gear assembly 14 positioned at the juncture of each column 12 and the platform 10. Thus, the supporting columns 12 may be individually oriented to produce the maximum in wave induced energy. If desired, each column can be independently controlled with separate mechanisms and sensing devices.

In order to permit the platform operator to control each supporting column individually for purposes of maximizing either propulsive thrust or turning moment, each vertical column will require a suitable rotating mechanism including thrust type bearing support at the built-in end of the column. A worm drive gear assembly appears appropriate for greatest mechanical efficiency in most installations.

MODE OF APPLICATION In a typical mode of application, the platform may be oriented directionally, a rotating moment in the horizontal plane would be produced by setting all supporting columns so as to produce moments about the platform center of gravity all acting in the same rotational sense, FIG. 7.

In order to develop the maximum station keeping thrust, each supporting column in the array should be individually oriented in the .wave system to produce the maximum wave induced drag component opposing the adverse wind-water current. FIG. 7 illustrates a typical combination of wind, water current and wave directions along with the corresponding instantaneous deployment of supporting columns for achieving the desired station keeping or maneuvering objective.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is: 1. Apparatus for maintaining the position and buoyancy of floating ocean bases comprising:

a. a platform positioned above the ocean surface; b. a plurality of buoyant and rotatable supporting columns attached to the under surface of said platform and extending vertically into the ocean;

at least some of said columns having a nonsymmetric cross-section with a portion of the periphery being concave; wave energy being extracted by said appropriately arranged columns from a wave train to assist in maintaining the position of said platform; means to rotate the vertical columns about their axis so as to derive. the maximum hydrodynamic force vectors which oppose any wind and current vectors tending to disturb positioning of the platform, said means for rotating the columns including: l. a sensing device attached to each column to determine variations in wave energy; 2. a computer means connected to the platform and adapted to receive the signal from said sensing device; 3. a motor controlled by said computer; and 4. a gear assembly positioned at the juncture of each column and the platform, said gear assembly adapted to orient each supporting column so as to extract the maximum in wave energy for assisting in maintaining the position of the platform. 2. The apparatus as defined in claim 1 wherein: the concave portion of said columns extends vertically at least the submerged length thereof. 3. The apparatus as defined in claim 1 wherein: the concave portion of said columns extends vertically the entire length thereof to take advantage of both wind and wave energy. 

1. Apparatus for maintaining the position and buoyancy of floating ocean bases comprising: a. a platform positioned above the ocean surface; b. a plurality of buoyant and rotatable supporting columns attached to the under surface of said platform and extending vertically into the ocean; c. at least some of said columns having a non-symmetric crosssection with a portion of the periphery being concave; d. wave energy being extracted by said appropriately arranged columns from a wave train to assist in maintaining the position of said platform; e. means to rotate the vertical columns about their axis so as to derive the maximum hydrodynamic force vectors which oppose any wind and current vectors tending to disturb positioning of the platform, said means for rotating the columns including:
 1. a sensing device attached to each column to determine variations in wave energy;
 2. a computer means connected to the platform and adapted to receive the signal from said sensing device;
 3. a motor controlled by said computer; and
 4. a gear assembly positioned at the juncture of each column and the platform, said gear assembly adapted to orient each supporting column so as to extract the maximum in wave energy for assisting in maintaining the position of the platform.
 2. a computer means connected to the platform and adapted to receive the signal from said sensing device;
 2. The apparatus as defined in claim 1 wherein: the concave portion of said columns extends vertically at least the submerged length thereof.
 3. The apparatus as defined in claim 1 wherein: the concave portion of said columns extends vertically the entire length thereof to take advantage of both wind and wave energy.
 3. a motor controlled by said computer; and
 4. a gear assembly positioned at the juncture of each column and the platform, said gear assembly adapted to orient each supporting column so as to extract the maximum in wave energy for assisting in maintaining the position of the platform. 